1. Field of Invention
The present invention relates to a connection structure providing an electrical connection between substrates of high-frequency circuit substrates in which high-frequency electronic components are packaged in a high-frequency electronic device processing a high-frequency signal such as microwave, millimeter wave or the like. The invention also relates to a method for manufacturing the mentioned connection structure and to a high-frequency circuit device constructed of the high-frequency circuit substrate and the connection structure.
2. Description of the Related Art
It is an essential requirement that electronic circuit such as commercial communication apparatus, satellite, radar, etc., which are used in a high-frequency radio frequency band of, e.g., X band (5.2-10.9 GHz) and K band (10.9-36.0 GHz), are low in loss and high in reliability.
Particularly, as a high-frequency circuit substrate packaged with high-frequency electronic components, a ceramic substrate of a low dielectric loss and a printed wiring board made of a fluorocarbon resin or BT (bismaleimid triazine) resin have been commonly utilized.
As to a high-frequency circuit substrate packaged with high-frequency electronic components, it is often the case that a plurality of high-frequency circuit substrates are connected and used for reasons of design or circuit assembly.
When connecting such high-frequency circuits to each other, connection with the use of a connector and cable is carried out commonly and generally in order to maintain the above-mentioned low loss and high reliability.
However, a connection structure using the connector and cable brings about the following problems.
A problem exists in that a machining cost becomes exceedingly high as well as downsizing is not easy since a connector consisting of a large number of precision components is manufactured by machining.
Another problem exists in that use of cables causes bulky connection portions, or incapability of weight saving.
Therefore, a connection method without use of any connector and cable has been devised for the purpose of achieving reduction in cost and size.
Connection between the high-frequency circuit substrates is not achieved just by connecting the substrates to each other through a conductor. A further problem exists in that sufficient electrical characteristic cannot be achieved without obtaining matching in the light of a high-frequency circuit.
Consequently, a still further problem exists in that a low-cost connection method used in a low-frequency circuit cannot be applied to the connection of a high-frequency circuit as it is.
On the other side, a further problem exists in that a long-term reliability cannot be preserved without absorbing or diminishing in any way a mechanical stress (i.e., heat stress) that is applied to a connection portion due to difference in linear expansion coefficient of the substrate or in connection structure due to change in ambient temperature.
An attempt for providing a connection between the substrates while satisfying electric characteristic and reliability has been proposed in the form of a connection structure, for example, in a patent document 1 (the Japanese Patent Publication (unexamined) No. 240601/1995.
As described in the above-mentioned patent document 1, this attempt is a method for implementing connection between two high-frequency circuit substrates, which are packaged onto a metal base, with the use of a connecting conductor molded in a semicircular shape.
To satisfy the electric characteristic, various types of conductors are devised.
That is, to deal with an impedance mismatch at a connection portion, a conductor for connection is formed into a plate shape, and conforms to a micro strip line in width.
Furthermore, a semicircular connection conductor 4 is packaged with a convex portion thereof facing to a metal base so as to be close to ground thereby causing an impedance mismatch to be smaller.
A heat stress generated at the connection portion due to temperature change and difference in linear expansion coefficient between the substrate and the connection conductor is to be absorbed or diminished by forming a connection conductor into a semicircular shape.
Meanwhile, the connection conductor, which is a single metal strip as shown in the patent document 1, is hard to be handled.
Although depending on conditions at the time of designing a circuit, the connection conductor becomes a minute part, which is several dozen to several hundred xcexcm square, thereby making it hard to handle.
For the same reason, operations for positioning and accurately packaging the connection conductor at a predetermined place on a high-frequency circuit substrate come to be extremely difficult.
Electrically, in the case where structure of the high-frequency transmission line is designed as a micro strip line, connection can be performed only with one part (connection conductor). For applying the connection conductor to a coplanar transmission line, however, three parts have to be used.
In addition, a coplanar transmission line is a type of transmission line processing a high-frequency signal, that is, a form in which ground potential parts (GND electrodes) are disposed adjacent on both sides of the high-frequency signal line.
Accordingly, to provide a connection between the substrates of the coplanar transmission line, required are one connection conductor acting as a connection conductor for mutually connecting the high-frequency signal lines and two connection conductors for connecting together the ground potential parts (GND electrodes) located on both sides of the high-frequency signal line.
It is extremely difficult to package a large number of such separate minute parts (i.e., connection conductors) close to one another.
Particularly in the case of joining them by soldering, e.g., movement of parts due to surface tension at the time of solder fusion should be taken into consideration.
Furthermore, in terms of function to absorb or diminish a heat stress, a semicircular connection conductor cannot be used in the case where interval between the substrates is narrow since the connection conductor is constructed so as to absorb or diminish a stress, which is applied to a connection portion, at a semicircular portion thereof.
Likewise, in the case where the substrate is thin, and distance between the micro strip line on the upper surface of the substrate and the metal base is small, a semicircular height portion of the connection conductor comes to be an obstacle without any sufficient level difference, thereby making it hard to package the semicircular connection conductor.
Furthermore, the packaging employs a method of connecting the substrates at the end portions thereof, and therefore it is necessary to form a transmission line such as micro strip line possessing high dimension accuracy up to the end portion of the substrate.
To realize this, routing is required since an inexpensive substrate machining such as punching, which renders poor finish accuracy at the end portion of the substrate.
When machining with a router the substrate on which a conductor resides up to the end portion, a copper foil at the machined portion may be turned up thereby making it difficult to secure accuracy at the end portion.
In addition, routing is a type of machining with the use of a NC (numerical control) router machine, which is a method for machining an article to be processed by feeding a rotating tool provided with spiral blades to the article.
Therefore, it is certainly possible to process an article with high accuracy even if it is of a complicated configuration. But there is a disadvantage of high machining cost since an expensive working machine is used.
Further, in the high-frequency circuit substrate that is a component of the high-frequency device, deformation such as warp, torsion or wave often occurs depending on manufacturing conditions or production lot regardless of an organic material or inorganic material. Such occurrence of deformation is a difference from the case where a high-frequency circuit substrate is made of a metallic material.
Furthermore, it is often the case that adjacent substrates are not in the same thickness due to a subtle difference in finish thereof or requirement for performing an impedance matching. There may be an occasion that a level difference of not less than several hundred xcexcm is produced between the substrates.
As a result, in the conventional example as shown in the patent document 1, there may be a case where an electrical conduction cannot be obtained (open state) between the substrates in certain packaging conditions.
For example, when sucking a connection conductor with the use of a vacuum suction collet provided with a flat surface and trying to package the connection conductor onto the uneven connection portion by soldering, an open fault may occur such that only the higher level substrate is connected, leaving the lower level substrate not electrically connected.
This occurrence of the open fault makes it impossible to normally transmit an electrical signal of a high frequency, whereby an object of providing an electrical connection between the substrates is impaired.
To solve such a problem, it is required to provide a mechanism that eliminates a level difference.
Furthermore, since there are many cases where an expensive semiconductor or components, which are made of expensive materials, are packaged in a high-frequency circuit substrate, a higher cost is inevitable.
Accordingly, in the case of occurrence of any malfunction at any circuit or component, it is desirable that the circuit board is detachable so that the circuit substrate may be repaired or replaced as much as possible.
To realize this, an easily detachable structure is required.
In the known art as shown in the patent document 1, a disadvantage exits in that a local repair work is extremely hard to be done since a minute connection construction is employed.
In short, to achieve a packaging construction to which such conventional art as described above is applied induces a complicated work and a high cost due to decline in yield accompanied with the complicated work. After all, the packaging construction according to the conventional art lacks practicability in the case of manufacturing a product required for a mass production.
The present invention was made to solve the above-discussed problems, and a first object of the invention is to provide a connection structure in which positioning or handling of a connecting conductor (lead frame) becomes easy when connecting two coplanar high-frequency circuit substrates disposed in opposition, eventually resulting in high workability and productivity.
A second object of the invention is to provide a method for manufacturing the above-mentioned connection structure.
A third object of the invention is to provide a high-frequency circuit device, which possesses high assembly workability and productivity, or a high reliability over a long term despite change in ambient temperature, by providing a connection between the high-frequency circuit substrates using the above-mentioned connection structure.
A connection structure for a high-frequency circuit substrate according to the invention includes: a first high-frequency circuit substrate in which a first high-frequency transmission line is formed to an end on a substrate surface, and a first GND electrode is formed on both sides of the mentioned first high-frequency transmission line; and a second high-frequency circuit substrate in which a second high-frequency transmission line is formed to an end on a substrate surface, a second GND electrode is formed on both sides of the mentioned second high-frequency transmission line, and which is located coplanar with the mentioned first high-frequency circuit substrate; the mentioned first high-frequency circuit substrate and the second high-frequency circuit substrate being electrically connected.
The mentioned connection structure for the high-frequency circuit substrates further includes: a high-frequency transmission line lead frame for providing a connection between the end portion of the mentioned first high-frequency transmission line formed on the mentioned first high-frequency circuit substrate and the end portion of the mentioned second high-frequency transmission line formed on the mentioned second high-frequency circuit substrate; a plurality of GND electrode lead frames that are disposed in parallel to the mentioned high-frequency transmission line lead frame on both sides of the mentioned high-frequency transmission line lead frame, and that provides a connection between the mentioned first GND electrode on the mentioned first high-frequency circuit substrate and the mentioned second GND electrode on the mentioned second high-frequency circuit substrate; and a reinforcing substrate for integrally securing the mentioned high-frequency transmission line lead frame and a plurality of the mentioned GND electrode lead frames.
Thus, in the connection structure for a high-frequency circuit substrate according to the invention, positioning and handling of the high-frequency transmission line lead frame and a plurality of GND electrode lead frames acting as the connection conductors come to be easy at the time of electrically connecting together the two high-frequency circuit substrates disposed in opposition. As a result, connection between the high-frequency circuit substrates can be carried out in such a manner as to achieve a high workability and productivity.
A manufacturing method of a connection structure for a high-frequency circuit substrate according to the invention includes the steps of:
molding a high-frequency transmission line lead frame and a plurality of GND electrode lead frames into a comb shape of end portions being common by press working employing a metal plate having a predetermined resilience;
positioning the high-frequency transmission line lead frame and a plurality of GND electrode lead frames, which have been molded in a comb shape, to come to a predetermined position on the reinforcing substrate, and fixing them together at the predetermined position;
molding the high-frequency transmission line lead frame and a plurality of GND electrode lead frames, which have been fixed at the mentioned predetermined position on the mentioned reinforcing substrate, into a predetermined configuration by press working; and
cutting a remainder of the high-frequency transmission line lead frame and a plurality of GND electrode lead frames, which have been fixed at a predetermined position on the mentioned reinforcing substrate and molded into a predetermined configuration by press working.
In the mentioned manufacturing method of a connection structure for a high-frequency circuit substrate according to the invention, positioning and handling of the high-frequency transmission line lead frame and a plurality of GND electrode lead frames acting as the connection conductors come to be easy at the time of electrically connecting together the two high-frequency circuit substrates oppositely disposed. As a result, a manufacturing method of a connection structure capable of providing a connection between the high-frequency circuit substrates is established in such a manner as to achieve a high workability and productivity.
A high-frequency circuit device according to the invention includes:
a first high-frequency circuit substrate, which is disposed on a metal base, at which a first high-frequency transmission line is formed to an end on a substrate surface, and a first GND electrode is formed on both sides of the mentioned first high-frequency transmission line;
a second high-frequency circuit substrate at which a second high-frequency transmission line is formed to an end on a substrate surface, and a second GND electrode is formed on both sides of the mentioned second high-frequency transmission line, the mentioned second high-frequency circuit substrate being disposed opposite to the mentioned first high-frequency circuit substrate on the mentioned metal base; and
a connection structure for a high-frequency circuit substrate according to any of claims 1 through 7.
In the high-frequency circuit device of above construction, positioning and handling of the high-frequency transmission line lead frame and a plurality of GND electrode lead frames acting as the connection conductors come to be easy at the time of electrically connecting the two high-frequency circuit substrates disposed in opposition. As a result, connection between the high-frequency circuit substrates can be carried out in such a manner as to achieve a high workability and productivity thereby enabling to provide a high-frequency circuit device of a low price and a high reliability.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.